Pfizer's Alpharma subsidiary in the US planned to take much the same action starting early this month in response to a request from the US Food and Drug Administration (FDA), citing its own study of the drug.

Arsenic content

According to a notice from Health Canada's Veterinary Drugs Directorate, the FDA study had found inorganic arsenic, a known carcinogen, at higher levels in the livers of chickens treated with the Nitro drugs, compared with untreated chickens.

Health Canada said it had reviewed the FDA study and agrees with its conclusion that the levels of inorganic arsenic involved were "very low" and posed no immediate health risk to people eating meat from birds treated with the drugs.

Rather, Health Canada said, the suspension of sales is "a precautionary measure to remove any avoidable exposure to very low levels of inorganic arsenic in chickens treated with roxarsone."